One-step production of a polypropylene composition

ABSTRACT

The present invention relates to a process for providing a polypropylene composition comprising a branched polypropylene (b-PP), a polypropylene composition as well as a film comprising the polypropylene composition.

The present invention relates to a process for providing a polypropylenecomposition comprising a branched polypropylene (b-PP), a polypropylenecomposition as well as a film comprising the polypropylene composition.

High melt strength polypropylene (HMS-PP) compositions are generallyknown in the art. EP 0 879 830, filed by Borealis in 1997, describes thebasics of the Borealis high melt strength (HMS) post-reactor processwhere peroxide and butadiene are used to make long chain branchedpolypropylene (LCB-PP) materials. This patent covers a wide range ofpowder melt flow rates (MFRs) and particle sizes.

One of the biggest challenges within the existing commercially availablehigh melt strength polypropylene (HMS-PP) compositions based HMSextrusion coating grades, such as the WF420HMS grade, is their ratherhigh time- and cost-consuming production together with varying filmquality. This is because the commercially available coating grades aretypically produced in a two-step process. In a first step, apolypropylene composition is prepared in a HMS line and in a secondstep, the obtained product is then vis-broken to increase the melt flowrate (MFRs). The increase of melt flow rate (MFRs) is required todecrease the OCS gel index and to obtain a suitable MFR for extrusioncoating.

There remains a need in the art for a less time- and cost-consumingprocess to produce polypropylene compositions, like high melt strengthpolypropylene (HMS-PP), of reliable and/or improved properties.

Accordingly, the object of the present invention is to provide a processwhich enables a skilled person to produce a polypropylene compositionand a film made of said polypropylene composition having better filmquality in a cost- and time-efficient way compared to the respectivecommercially available coating grade.

The present inventors now surprisingly found out that a polypropylenecomposition having specific properties such as a desired melt flow rateMFR₂ (230° C.) at high F₃₀ melt strength and v₃₀ melt extensibility, canbe produced in a single step process without implementing a subsequentvis-breaking step. Furthermore, it was found that the obtainedpolypropylene composition and films made therefrom provide better filmqualities expressed by a low OCS gel index compared to the respectivecommercially available coating grade.

Thus, the present invention relates to a process for providing apolypropylene composition comprising a branched polypropylene (b-PP),the process comprises the steps of:

a) providing a polypropylene (PP) having a melt flow rate MFR₂ (230° C.)of more than 1.0 g/10 min;

-   -   b) providing a thermally decomposing free radical-forming agent,    -   c) providing bifunctionally unsaturated monomer(s) and/or        multifunctionally unsaturated low molecular weight polymer(s),    -   d) providing a linear polypropylene (l-PP) having a melt flow        rate MFR₂ (230° C.) of 10.0 to 50.0 g/10 min,    -   e) reacting the polypropylene (PP) of step a) with the thermally        decomposing free radical-forming agent of step b) and the        bifunctionally unsaturated monomer(s) and/or multifunctionally        unsaturated low molecular weight polymer(s) of step c) obtaining        thereby the branched polypropylene (b-PP), and    -   f) reacting the branched polypropylene (b-PP) obtained in        step e) with the linear polypropylene (l-PP) of step d), wherein        the polypropylene composition and/or branched polypropylene        (b-PP) has/have    -   i) a melt flow rate MFR₂ (230° C.) measured according to ISO        1133 of 18.0 to 35.0 g/10 min,    -   ii) a F₃₀ melt strength of more than 3.4 cN and a v₃₀ melt        extensibility of more than 200 mm/s, wherein the F₃₀ melt        strength and the v₃₀ melt extensibility are measured according        to ISO 16790:2005.

The present invention further provides a polypropylene compositioncomprising

-   -   (a) 95.0 to 99.0 parts by weight of a branched polypropylene        (b-PP); and    -   (b) 1.0 to 5.0 parts by weight of a linear polypropylene (l-PP)        having a melt flow rate MFR₂ (230° C.) measured according to ISO        1133 of 10.0 to 50.0 g/10 min, preferably from 20.0 to 40.0 g/10        min;    -   wherein the polypropylene composition has        -   a melt flow rate MFR₂ (230° C.) measured according to ISO            1133 from 18.0 to 35.0 g/10 min, and        -   an OCS gel index of less than 2,500; and    -   wherein the polypropylene composition and/or the branched        polypropylene (b-PP) has/have a F₃₀ melt strength of more than        3.4 cN and a v₃₀ melt extensibility of more than 200 mm/s,        wherein the F₃₀ melt strength and the v₃₀ melt extensibility are        measured according to ISO 16790:2005.

It is preferred that the polypropylene composition comprises

-   -   (a) 95.0 to 99.0 parts by weight of a branched polypropylene        (b-PP); and    -   (b) 1.0 to 5.0 parts by weight of a linear polypropylene (l-PP)        having a melt flow rate MFR₂ (230° C.) measured according to ISO        1133 from 25.0 to 38.0 g/10 min;    -   wherein the polypropylene composition has        -   a melt flow rate MFR₂ (230° C.) measured according to ISO            1133 from 19.0 to 25.0 g/10 min, and        -   an OCS gel index of less than 2,000;    -   and wherein further the polypropylene composition and/or the        branched polypropylene (b-PP) has/have a F₃₀ melt strength from        4.0 to 20.0 cN and a v₃₀ melt extensibility from 240 to 300        mm/s, wherein the F₃₀ melt strength and the v₃₀ melt        extensibility are measured according to ISO 16790:2005.

It is further preferred that the polypropylene composition comprises atleast one additive (A) selected from the group consisting ofantioxidants, metal deactivators, UV-stabilizers, antistatic agents,antifogging agents, acid scavengers, blowing agents, cling agents,lubricants, nucleating agents, slip agents, antiblocking agents andmixtures thereof.

The present invention still further provides a film comprising thepolypropylene composition.

According to one embodiment of the present invention, the polypropylene(PP) has a melt flow rate MFR₂ (230° C.) measured according to ISO 1133in the range from 1.0 to 18.0 g/10 min and preferably in the range from1.0 to 15.0 g/10 min.

According to another embodiment of the present invention, thepolypropylene (PP) (a) is a linear polypropylene (l-PP′); and/or (b) isa linear polypropylene (l-PP′) having a F₃₀ melt strength of more than1.0 cN and a v₃₀ melt extensibility of below 200 mm/s, wherein the F₃₀melt strength and the v₃₀ melt extensibility are measured according toISO 16790:2005.

According to yet another embodiment of the present invention, (a) thethermally decomposing free radical-forming agent of step b) is aperoxide and/or (b) the bifunctionally unsaturated monomer(s) and/ormultifunctionally unsaturated low molecular weight polymer(s) of step c)is/are selected from the group consisting of divinyl compounds, allylcompounds and dienes.

According to one embodiment of the present invention, (a) the linearpolypropylene (l-PP) of step d) has a melt flow rate MFR₂ (230° C.)measured according to ISO 1133 from 20.0 to 40.0 g/10 min and preferablyfrom 25.0 to 38.0 g/10 min, and/or (b) the linear polypropylene (l-PP)of step d) comprises at least one additive (A), preferably two additives(A), selected from the group consisting of antioxidants, metaldeactivators, UV-stabilizers, antistatic agents, antifogging agents,acid scavengers, blowing agents, cling agents, lubricants, nucleatingagents, slip agents, antiblocking agents and mixtures thereof, and/or(c) the branched polypropylene (b-PP) obtained in step e) is free ofadditives (A).

According to another embodiment of the present invention, steps e) andf) are accomplished in an extruder, said extruder comprises in operationdirection a first mixing zone (MZ1) and a second mixing zone (MZ2),wherein further step e) takes place in the first mixing zone (MZ1)whereas step f) takes place in the second mixing zone (MZ2).

According to yet another embodiment of the present invention, theextruder comprises in operation direction a feed-throat (FT), the firstmixing zone (MZ1), the second mixing zone (MZ2) and a die (D), whereinbetween the first mixing zone (MZ1) and the second mixing zone (MZ2) aside feed-throat (SFT) is located, wherein further the polypropylene(PP) of step a), the thermally decomposing free radical-forming agent ofstep b), and the bifunctionally unsaturated monomer(s) and/ormultifunctionally unsaturated low molecular weight polymer(s) of step c)are fed via the feed-throat (FT) and the linear polypropylene (1-PP) ofstep d) is fed via the side feed-throat (SFT).

According to one embodiment of the present invention, not more than 10.0wt.-% of the total amount of the branched polypropylene (b-PP) of thepolypropylene composition is produced in the second mixing zone (MZ2).

According to another embodiment of the present invention, 1.0 to 6.0parts by weight of the linear polypropylene (l-PP) are added to 94.0 to99.0 parts by weight of branched polypropylene (b-PP), preferablywherein 1.0 to 3.0 parts by weight of the linear polypropylene (l-PP)are added to 97.0 to 99.0 parts by weight of branched polypropylene(b-PP), more preferably wherein 2.0 parts by weight of the linearpolypropylene (l-PP) are added to 98.0 parts by weight of branchedpolypropylene (b-PP).

According to yet another embodiment of the present invention, theresulting polypropylene composition and/or branched polypropylene (b-PP)(a) has/have a melt flow rate MFR₂ (230° C.) measured according to ISO1133 of 19.0 to 30.0 g/10 min, and/or (b) has/have a F₃₀ melt strengthfrom 4.0 to 20.0 cN and a v₃₀ melt extensibility from 240 to 300 mm/s,wherein the F₃₀ melt strength and the v₃₀ melt extensibility aremeasured according to ISO 16790:2005; and/or (c) has/have an OCS gelindex of less than 2,500 and preferably of less than 2,000.

According to one embodiment of the present invention, the resultingpolypropylene composition is prepared in a single step process.

In the following, the invention is described in more detail.

First the individual components provided in the instant invention, i.e.the branched polypropylene (b-PP), the polypropylene (PP), the thermallydecomposing free radical-forming agent, the bifunctionally unsaturatedmonomer(s) and/or multifunctionally unsaturated low molecular weightpolymer(s), the linear polypropylene (l-PP), and the optional additives(A), as well as the polypropylene composition are described.Subsequently process steps e) and f) as well as the inventive film aredescribed in more detail. However any information or any preferredembodiment provided for the individual components or the polypropylenecomposition is also applicable for the inventive process and film, ifreference is made to the individual components and the polypropylenecomposition, respectively.

The major component for the polypropylene composition to be providedaccording to the invention is a branched polypropylene (b-PP). Abranched polypropylene differs from a linear polypropylene in that thepolypropylene backbone covers side chains whereas a non-branchedpolypropylene, i.e. a linear polypropylene, does not cover side chains.The side chains have significant impact on the rheology of thepolypropylene. Accordingly linear polypropylenes and branchedpolypropylenes can be clearly distinguished by its flow behavior understress.

Branching can be achieved by using specific catalysts, i.e. specificsingle-site catalysts, or by chemical modification. Concerning thepreparation of a branched polypropylene obtained by the use of aspecific catalyst reference is made to EP 1 892 264. With regard to abranched polypropylene obtained by chemical modification it is referredto EP 0 879 830 A1. In such a case the branched polypropylene is alsocalled high melt strength polypropylene. Preferably the branchedpolypropylene (b-PP) of the instant invention is obtained by chemicalmodification as described in more detail below and thus is a high meltstrength polypropylene (HMS-PP).

Therefore, it is one requirement of the present invention that thebranched polypropylene (b-PP), preferably the high melt strengthpolypropylene (HMS-PP), as the major component of the polypropylenecomposition has a F₃₀ melt strength of more than 3.4 cN and a v₃₀ meltextensibility of more than 200 mm/s, wherein the F₃₀ melt strength andthe v₃₀ melt extensibility are measured according to ISO 16790:2005.

For example, the branched polypropylene (b-PP), preferably the high meltstrength polypropylene (HMS-PP), as the major component of thepolypropylene composition has a F₃₀ melt strength from 4.0 to 20.0 cNand a v₃₀ melt extensibility from 240 to 300 mm/s. Preferably, thebranched polypropylene (b-PP), preferably the high melt strengthpolypropylene (HMS-PP), as the major component of the polypropylenecomposition has a F₃₀ melt strength from 4.0 to 10.0 cN and a v₃₀ meltextensibility from 240 to 300 mm/s. The F₃₀ melt strength and the v₃₀melt extensibility are measured according to ISO 16790:2005.

Typically the instant polypropylene composition also has a F₃₀ meltstrength of more than 3.4 cN and a v₃₀ melt extensibility of more than200 mm/s, preferably has a F₃₀ melt strength from 4.0 to 20.0 cN and av₃₀ melt extensibility from 240 to 300 mm/s. For example, the instantpolypropylene composition has a F₃₀ melt strength from 4.0 to 10.0 cNand a v₃₀ melt extensibility from 240 to 300 mm/s. The F₃₀ melt strengthand the v₃₀ melt extensibility are measured according to ISO 16790:2005.

In order to provide a sufficient MFR for extrusion coating, one furtherrequirement of the present invention is that the branched polypropylene(b-PP), preferably the high melt strength polypropylene (HMS-PP), as themajor component of the polypropylene composition has a melt flow rateMFR₂ (230° C.) measured according to ISO 1133 of 18.0 to 35.0 g/10 min.For example, the branched polypropylene (b-PP), preferably the high meltstrength polypropylene (HMS-PP), as the major component of thepolypropylene composition has a melt flow rate MFR₂ (230° C.) measuredaccording to ISO 1133 of 19.0 to 30.0 g/10 min. Preferably, the branchedpolypropylene (b-PP), preferably the high melt strength polypropylene(HMS-PP), as the major component of the polypropylene composition has amelt flow rate MFR₂ (230° C.) measured according to ISO 1133 of 19.0 to25.0 g/10 min.

It is thus also preferred that the instant polypropylene compositionalso has a melt flow rate MFR₂ (230° C.) measured according to ISO 1133of 18.0 to 35.0 g/10 min. For example, the instant polypropylenecomposition has a melt flow rate MFR₂ (230° C.) measured according toISO 1133 of 19.0 to 30.0 g/10 min. Alternatively, the instantpolypropylene composition has a melt flow rate MFR₂ (230° C.) measuredaccording to ISO 1133 of 19.0 to 25.0 g/10 min.

It is thus required that the branched polypropylene (b-PP), preferablythe high melt strength polypropylene (HMS-PP), as the major component ofthe polypropylene composition has

-   -   a) a F₃₀ melt strength of more than 3.4 cN and a v₃₀ melt        extensibility of more than 200 mm/s, wherein the F₃₀ melt        strength and the v₃₀ melt extensibility are measured according        to ISO 16790:2005, and    -   b) a melt flow rate MFR₂ (230° C.) measured according to ISO        1133 of 18.0 to 35.0 g/10 min.

It is preferred that the branched polypropylene (b-PP), preferably thehigh melt strength polypropylene (HMS-PP), as the major component of thepolypropylene composition has

-   -   a) a F₃₀ melt strength from 4.0 to 20.0 cN and a v₃₀ melt        extensibility from 240 to 300 mm/s, wherein the F₃₀ melt        strength and the v₃₀ melt extensibility are measured according        to ISO 16790:2005, and    -   b) a melt flow rate MFR₂ (230° C.) measured according to ISO        1133 of 19.0 to 30.0 g/10 min.

Alternatively, the branched polypropylene (b-PP), preferably the highmelt strength polypropylene (HMS-PP), as the major component of thepolypropylene composition has

-   -   a) a F₃₀ melt strength from 4.0 to 10.0 cN and a v₃₀ melt        extensibility from 240 to 300 mm/s, wherein the F₃₀ melt        strength and the v₃₀ melt extensibility are measured according        to ISO 16790:2005, and    -   b) a melt flow rate MFR₂ (230° C.) measured according to ISO        1133 of 19.0 to 25.0 g/10 min.

Furthermore, it is preferred that said branched polypropylene (b-PP),preferably the high melt strength polypropylene (HMS-PP), has an OCS gelindex of less than 2,500. Preferably, the branched polypropylene (b-PP),preferably the high melt strength polypropylene (HMS-PP), has an OCS gelindex of less than 2,000. For example, the branched polypropylene(b-PP), preferably the high melt strength polypropylene (HMS-PP), has anOCS gel index from 500 to 2,000.

It is thus also preferred that the instant polypropylene compositionalso has an OCS gel index of less than 2,500. For example, the instantpolypropylene composition has an OCS gel index of less than 2,000.Alternatively, the instant polypropylene composition has an OCS gelindex from 500 to 2,000.

Hence, in one specific embodiment, the branched polypropylene (b-PP),preferably the high melt strength polypropylene (HMS-PP), has

-   -   a) a F₃₀ melt strength of more than 3.4 cN and a v₃₀ melt        extensibility of more than 200 mm/s, preferably a F₃₀ melt        strength from 4.0 to 20.0 cN and a v₃₀ melt extensibility from        240 to 300 mm/s and most preferably a F₃₀ melt strength from 4.0        to 10.0 cN and a v₃₀ melt extensibility from 240 to 300 mm/s,        wherein the F₃₀ melt strength and the v₃₀ melt extensibility are        measured according to ISO 16790:2005,    -   and    -   b) a melt flow rate MFR₂ (230° C.) measured according to ISO        1133 of 18.0 to 35.0 g/10 min, preferably from 19.0 to 30.0 g/10        min and most preferably from 19.0 to 25.0 g/10 min,    -   and    -   c) an OCS gel index of less than 2,500, preferably of less than        2,000 and most preferably from 500 to 2,000.

Accordingly, also the instant polypropylene composition preferably has

-   -   a) a F₃₀ melt strength of more than 3.4 cN and a v₃₀ melt        extensibility of more than 200 mm/s, preferably a F₃₀ melt        strength from 4.0 to 20.0 cN and a v₃₀ melt extensibility from        240 to 300 mm/s and most preferably a F₃₀ melt strength from 4.0        to 10.0 cN and a v₃₀ melt extensibility from 240 to 300 mm/s,        wherein the F₃₀ melt strength and the v₃₀ melt extensibility are        measured according to ISO 16790:2005,    -   and    -   b) a melt flow rate MFR₂ (230° C.) measured according to ISO        1133 of 18.0 to 35.0 g/10 min, preferably from 19.0 to 30.0 g/10        min and most preferably from 19.0 to 25.0 g/10 min,    -   and    -   c) an OCS gel index of less than 2,500, preferably of less than        2,000 and most preferably from 500 to 2,000.

Preferably, the branched polypropylene (b-PP), preferably the high meltstrength polypropylene (HMS-PP), has a melting point of at least 130°C., more preferably of at least 135° C. and most preferably of at least140° C. The crystallization temperature is preferably at least 120° C.

Further, the branched polypropylene (b-PP), preferably the high meltstrength polypropylene (HMS-PP), can be a branched random propylenecopolymer (b-R-PP), preferably high melt strength random propylenecopolymer (R-HMS-PP), or a branched propylene homopolymer (b-H-PP),preferably a high melt strength propylene homopolymer (H-HMS-PP), thelatter being preferred.

For the purpose of the present invention, the expression “propylenehomopolymer” refers to a polypropylene that consists substantially, i.e.of at least 97 mol.-%, preferably of at least 98 mol.-%, more preferablyof at least 99 mol.-%, most preferably of at least 99.8 mol.-% ofpropylene units. In a preferred embodiment only propylene units in thepropylene homopolymer are detectable.

In case the branched polypropylene (b-PP), preferably the high meltstrength polypropylene (HMS-PP), is a branched random propylenecopolymer (b-R-PP), preferably a high melt strength random propylenecopolymer (R-HMS-PP), it comprises monomers copolymerizable withpropylene, for example comonomers such as ethylene and/or C₄ to C₁₂α-olefins, in particular ethylene and/or C₄ to C₁₀ α-olefins, e.g.1-butene and/or 1-hexene. Preferably the branched random propylenecopolymer (b-R-PP), preferably the high melt strength random propylenecopolymer (R-HMS-PP), comprises, especially consists of, monomerscopolymerizable with propylene from the group consisting of ethylene,1-butene and 1-hexene. More specifically the branched random propylenecopolymer (b-R-PP), preferably the high melt strength random propylenecopolymer (R-HMS-PP), comprises—apart from propylene—units derivablefrom ethylene and/or 1-butene. In a preferred embodiment the branchedrandom propylene copolymer (b-R-PP), preferably the high melt strengthrandom propylene copolymer (R-HMS-PP), comprises units derivable fromethylene and propylene only. The comonomer content in the branchedrandom propylene copolymer (b-R-PP), preferably in the high meltstrength random propylene copolymer (R-HMS-PP), is preferably in therange of more than 0.2 to 10.0 mol.-%, still more preferably in therange of more than 0.5 to 7.0 mol.-%.

In this regard, it is to mention that the high melt strengthpolypropylene (HMS-PP) being either a high melt strength propylenehomopolymer (H-HMS-PP) or a high melt strength random propylenecopolymer (R-HMS-PP) may comprise additionally unsaturated monomersdifferent to the comonomers defined for the high melt strength randompropylene copolymer (R-HMS-PP). In other words the high melt strengthpropylene homopolymer (H-HMS-PP) or the high melt strength randompropylene copolymer (R-HMS-PP) may comprise unsaturated monomersintroduced by chemical modification, like bifunctionally unsaturatedmonomer(s) and/or multifunctionally unsaturated low molecular weightpolymer(s) as defined in detail below, being different to propylene,ethylene and other C₄ to C₁₂ α-olefins. Accordingly the definition ofhomopolymer and copolymer in view of the high melt strengthpolypropylene (HMS-PP) refers actually to the unmodified polypropyleneused to obtain the melt strength polypropylene (HMS-PP) by chemicalmodification as defined in detail below.

As mentioned, the branched polypropylene (b-PP), when used in the formof a high melt strength polypropylene (HMS-PP) is a chemically modifiedpolypropylene. Accordingly the high melt strength polypropylene (HMS-PP)can be further defined by the way obtained. The high melt strengthpolypropylene (HMS-PP) is preferably the result of treating anunmodified polypropylene with thermally decomposing radical-formingagents and/or with ionizing radiation. However in such a case a highrisk exists that the unmodified polypropylene is degraded, which isdetrimental. Thus, it is preferred that the modification is accomplishedby the use of bifunctionally unsaturated monomer(s) and/ormultifunctionally unsaturated low molecular weight polymer(s) aschemically bound bridging unit(s). A suitable method to obtain a highmelt strength polypropylene (HMS-PP) is for instance disclosed in EP 0787 750, EP 0 879 830 A1 and EP 0 890 612 A2. All documents are herewithincluded by reference. Thereby, the amount of peroxide is preferably inthe range of 0.05 to 3.00 wt.-% based on the unmodified polypropylene.

Accordingly in one preferred embodiment the high melt strengthpolypropylene (HMS-PP) comprises

-   -   (a) if it is a high melt strength propylene homopolymer        (H-HMS-PP) units derived from        -   (i) propylene and        -   (ii) bifunctionally unsaturated monomer(s) and/or            multifunctionally unsaturated low molecular weight            polymer(s), or    -   (b) if it is a high melt strength random propylene copolymer        (R-HMS-PP) units derived from        -   (i) propylene        -   (ii) ethylene and/or C₄ to C₁₀ α-olefins, e.g. 1-butene            and/or 1-hexene, preferably erthylene, and        -   (iii) bifunctionally unsaturated monomer(s) and/or            multifunctionally unsaturated low molecular weight            polymer(s),

The branched polypropylene (b-PP), i.e. the high melt strengthpolypropylene (HMS-PP), may contain more than one bifunctionallyunsaturated monomer and/or multifunctionally unsaturated low molecularweight polymer. Even more preferred the amount of bifunctionallyunsaturated monomer(s) and/or multifunctionally unsaturated lowmolecular weight polymer(s) together in the branched polypropylene(b-PP), i.e. in the high melt strength polypropylene (HMS-PP), is 0.01to 10.0 wt.-% based on said branched polypropylene (b-PP), i.e. based onsaid high melt strength polypropylene (HMS-PP).

In a preferred embodiment the branched polypropylene (b-PP), i.e. thehigh melt strength polypropylene (HMS-PP), is free of additives (A).Accordingly in case the instant polypropylene composition comprisesadditives (A), these additives (A) are not brought in the polypropylenecomposition during the manufacture of the branched polypropylene (b-PP),i.e. of the high melt strength polypropylene (HMS-PP).

According to step a) of the instant process a polypropylene (PP) havinga melt flow rate MFR₂ (230° C.) of more than 1.0 g/10 min is provided.

As mentioned above, the branched polypropylene (b-PP), i.e. the highmelt strength polypropylene (HMS-PP), is a modified polypropylene, whichis obtained by reacting the polypropylene (PP) with a thermallydecomposing free radical-forming agent and with bifunctionallyunsaturated monomer(s) and/or with multifunctionally unsaturated lowmolecular weight polymer(s) as well as a linear polypropylene (l-PP).

Essential aspect of the invention is that a specific unmodifiedpolypropylene (PP) must be used in the present invention for themanufacture of the branched polypropylene (b-PP), i.e. of the high meltstrength polypropylene (HMS-PP), and thus for the manufacture of thepolypropylene composition comprising the branched polypropylene (b-PP),i.e. comprising the high melt strength polypropylene (HMS-PP). Aparticular finding is that the polypropylene (PP), preferably a linearpolypropylene (l-PP′), must have a rather low molecular weight and thusa rather high melt flow rate. Accordingly, it is required that thepolypropylene (PP), preferably the linear polypropylene (l-PP′), has amelt flow rate MFR₂ (230° C.) measured according to ISO 1133 of morethan 1.0 g/10 min, preferably in the range from 1.0 to 18.0 g/10 min,like in the range from 1.0 to 15.0 g/10 min. For example, thepolypropylene (PP), preferably the linear polypropylene (l-PP′), has amelt flow rate MFR₂ (230° C.) measured according to ISO 1133 in therange from 1.5 to 15.0 g/10 min, preferably in the range from 2.0 to15.0 g/10 min, more preferably in the range from 3.0 to 13.0 g/10 minand most preferably in the range from 3.0 to 10.0 g/10 min.

The branched polypropylene (b-PP), i.e. the high melt strengthpolypropylene (HMS-PP), differs from the polypropylene (PP) which isused for its manufacture that the backbone of the branched polypropylene(b-PP), i.e. of the high melt strength polypropylene (HMS-PP), coversside chains whereas the starting product, i.e. the polypropylene (PP),preferably the linear polypropylene (l-PP′), does not cover or nearbydoes not cover side chains. The side chains have significant impact onthe rheology of the polypropylene. Accordingly, the starting product,i.e. the polypropylene (PP), preferably the linear polypropylene(l-PP′), and the obtained branched polypropylene (b-PP), i.e. the highmelt strength polypropylene (HMS-PP), can be clearly distinguished byits flow behavior under stress.

Furthermore, as already mentioned above the polypropylene (PP) ispreferably a linear polypropylene (l-PP′). The same considerations applyto the linear polypropylene (l-PP) as discussed in detail below.Accordingly, throughout the instant invention, the term “linearpolypropylene” indicates that the linear polypropylene, shows no ornearby no-branching structure. Due to the absence of branches, thelinear polypropylenes, i.e. the linear polypropylene (l-PP) and thelinear polypropylene (l-PP′), are preferably featured by a low v₃₀ meltextensibility and/or a low F₃₀ melt strength.

Thus, it is preferred that the polypropylene (PP), preferably the linearpolypropylene (l-PP′), has

-   -   (a) a F₃₀ melt strength of more than 1.0 cN, preferably of more        than 2.0 cN, more preferably in the range of 1.0 to 65.0 cN,        still more preferably in the range of 1.5 to 50.0 cN, yet more        preferably in the range of 2.0 to 50.0 cN, still yet more        preferably in the range of 2.5 to 50.0 cN like in the range of        2.5 to 30 cN;

and

-   -   (b) a v₃₀ melt extensibility of below 200 mm/s, preferably of        below 190 mm/s, more preferably in the range of 100 to below 200        mm/s, still more preferably in the range of 120 to 190 mm/s, yet        more preferably in the range of 120 to 175 mm/s, like in the        range of 125 to 170 mm/s, wherein the F₃₀ melt strength and the        v₃₀ melt extensibility are measured according to ISO 16790:2005.

In other words it is preferred that the polypropylene (PP), preferablythe linear polypropylene (l-PP′), has a F₃₀ melt strength of more than1.0 cN and a v₃₀ melt extensibility of below 200 mm/s, preferably a F₃₀melt strength of more than 2.0 cN and a v₃₀ melt extensibility of below190 mm/s, more preferably a F₃₀ melt strength in the range of 1.0 to65.0 cN and a v₃₀ melt extensibility in the range of 100 to below 200mm/s, yet more preferably a F₃₀ melt strength in the range of 2.0 to50.0 cN and in the range of 120 to 190 mm/s, still yet more preferably aF₃₀ melt strength in the range of 2.5 to 50.0 cN and in the range of 120to 175 mm/s, like a F₃₀ melt strength in the range of 2.5 to 30.0 cN anda v₃₀ melt extensibility in the range of 125 to 170 mm/s, wherein theF₃₀ melt strength and the v₃₀ melt extensibility are measured accordingto ISO 16790:2005.

Accordingly, in one specific embodiment the polypropylene (PP),preferably the linear polypropylene (l-PP′), has

-   -   (a) a melt flow rate MFR₂ (230° C.) measured according to ISO        1133 of more than 1.0 g/10 min, preferably in the range from 1.0        to 18.0 g/10 min, more preferably in the range from 1.0 to 15.0        g/10 min, still more preferably in the range from 1.5 to 15.0        g/10 min, yet more preferably in the range from 2.0 to 15.0 g/10        min, even more preferably in the range from 3.0 to 13.0 g/10 min        and most preferably in the range from 3.0 to 10.0 g/10 min; and    -   (b) a F₃₀ melt strength of more than 1.0 cN, preferably of more        than 2.0 cN, more preferably in the range of 1.0 to 65.0 cN,        still more preferably in the range of 1.5 to 50.0 cN, yet more        preferably in the range of 2.0 to 50.0 cN, still yet more        preferably in the range of 2.5 to 50.0 cN like in the range of        2.5 to 30 cN; and    -   (c) a v₃₀ melt extensibility of below 200 mm/s, preferably of        below 190 mm/s, more preferably in the range of 100 to below 200        mm/s, still more preferably in the range of 120 to 190 mm/s, yet        more preferably in the range of 120 to 175 mm/s, like in the        range of 125 to 170 mm/s, wherein the F₃₀ melt strength and the        v₃₀ melt extensibility are measured according to ISO 16790:2005.

Therefore, in one specific embodiment the polypropylene (PP) is a linearpolypropylene (1-PP′) having a melt flow rate MFR₂ (230° C.) of morethan 1.0 g/10 min, a F₃₀ melt strength of more than 1.0 cN and a v₃₀melt extensibility of below 200 mm/s, preferably a melt flow rate MFR₂(230° C.) in the range from 1.0 to 18.0 g/10 min, a F₃₀ melt strength ofmore than 2.0 cN and a v₃₀ melt extensibility of below 190 mm/s, morepreferably a melt flow rate MFR₂ (230° C.) in the range from 1.0 to 15.0g/10 min, a F₃₀ melt strength in the range of 1.0 to 65 cN and a v₃₀melt extensibility in the range of 100 to below 200 mm/s, yet morepreferably a melt flow rate MFR₂ (230° C.) in the range from 1.5 to 15.0g/10 min a F₃₀ melt strength in the range of 1.5 to 50 cN and in therange of 120 to 190 mm/s, still yet more preferably a melt flow rateMFR₂ (230° C.) in the range from 2.0 to 15.0 g/10 min, a F₃₀ meltstrength in the range of 2.0 to 50 cN and a v₃₀ melt extensibility inthe range of 120 to 175 mm/s, like a melt flow rate MFR₂ (230° C.) inthe range from 3.0 to 13.0 g/10 min a F₃₀ melt strength in the range of2.5 to 50 cN and a v₃₀ melt extensibility in the range of 120 to 175mm/s. For example, the polypropylene (PP) is a linear polypropylene(l-PP′) having a melt flow rate MFR₂ (230° C.) in the range from 3.0 to10.0 g/10 min a F₃₀ melt strength in the range of 2.5 to 30 cN and a v₃₀melt extensibility in the range of 125 to 170 mm/s.

Preferably, the polypropylene (PP), preferably the linear polypropylene(l-PP′), has a melting point of at least 140° C., more preferably of atleast 150° C. and still more preferably of at least 158° C. For example,the polypropylene (PP), preferably the linear polypropylene (l-PP′), hasa melting point in the range from 140° C. to 180° C., more preferably inthe range from 150° C. to 170° C. and most preferably in the range from158° C. to 165° C.

Additionally or alternatively, it is preferred that the polypropylene(PP), preferably the linear polypropylene (l-PP′), is used in form ofparticles of specific size. Accordingly it is preferred that thepolypropylene (PP), preferably the linear polypropylene (l-PP′), has

-   -   (a) a particle size distribution d₉₀ of below 1,500 μm; more        preferably below 1,000 μm, still more preferably in the range of        50 to below 1,000 μm, yet more preferably in the range of 100 to        800 μm, like in the range of 150 to 600 μm;    -   and/or    -   (b) a particle size distribution d₅₀ of below 1,000 μm; more        preferably below 800 μm, still more preferably in the range of        30 to below 1,000 μm, yet more preferably in the range of 50 to        600 μm, like in the range of 100 to 500 μm;    -   and/or    -   (c) a d₉₀/d₅₀ ratio of below 1.80, more preferably below 1.75,        still more preferably below 1.50, yet more preferably in the        range of 1.00 to 1.75, still yet more preferably in the range of        1.10 to 1.50.

The polypropylene (PP), preferably the linear polypropylene (l-PP′), canbe produced in a known manner for instance by employing a single-site ora Ziegler Natta catalyst. The polypropylene (PP), preferably the linearpolypropylene (l-PP′), is a propylene homopolymer (H-PP′), preferably alinear propylene homopolymer (1-H-PP′), or a propylene copolymer(R-PP′), preferably a linear propylene copolymer (1-R-PP′). For example,the polypropylene (PP), preferably the linear polypropylene (l-PP′), isa propylene homopolymer (H-PP′). Concerning the comonomer content andtype of comonomer it is referred to the information provided above forthe branched polypropylene (b-PP), especially it is referred to the highmelt strength random propylene copolymer (R-HMS-PP). Preferably thepolypropylene (PP) is a linear polypropylene (l-PP′). Still morepreferably the polypropylene (PP) is a linear propylene homopolymer(1-H-PP′). Accordingly all information provided with regard to melt flowrate MFR₂ (230° C.), melting point, F₃₀ melt strength, v₃₀ meltextensibility, and particle size and particle size distribution,respectively, applies especially for the linear polypropylene (l-PP′)and the linear propylene homopolymer (1-H-PP′).

In a preferred embodiment the polypropylene (PP), preferably the linearpolypropylene (1-PP′), is free of additives (A). Accordingly in case theinstant polypropylene composition comprises additives (A), theseadditives (A) are not brought in the polypropylene composition duringthe manufacture of the branched polypropylene (b-PP), i.e. of the highmelt strength polypropylene (HMS-PP).

According to step b) of the instant process a thermally decomposing freeradical-forming agent is provided.

Reaction of the bifunctionally unsaturated monomer(s) and/ormultifunctionally unsaturated low molecular weight polymer(s) with theunmodified polypropylene (PP), preferably the linear polypropylene(l-PP′), is performed in the presence of a thermally decomposing freeradical-forming agent, like a thermally decomposable peroxide and/orionizing radiation or microwave radiation.

Peroxides are preferred thermally decomposing free radical-formingagents. More preferably the thermally decomposing free radical-formingagent is selected from the group consisting of acyl peroxide, alkylperoxide, hydroperoxide, perester and peroxycarbonate.

The following listed peroxides are in particular preferred:

Acyl peroxides: benzoyl peroxide, 4-chlorobenzoyl peroxide,3-methoxybenzoyl peroxide and/or methyl benzoyl peroxide.

Alkyl peroxides: allyl t-butyl peroxide, 2,2-bis(t-butylperoxybutane),1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane,n-butyl-4,4-bis(t-butylperoxy) valerate, diisopropylaminomethyl-t-amylperoxide, dimethylaminomethyl-t-amyl peroxide,diethylaminomethyl-t-butyl peroxide, dimethylaminomethyl-t-butylperoxide, 1,1-di-(t-amylperoxy)cyclohexane, t-amyl peroxide,t-butylcumyl peroxide, t-butyl peroxide and/or 1-hydroxybutyl n-butylperoxide.

Peresters and peroxy carbonates: butyl peracetate, cumyl peracetate,cumyl perpropionate, cyclohexyl peracetate, di-t-butyl peradipate,di-t-butyl perazelate, di-t-butyl perglutarate, di-t-butyl perthalate,di-t-butyl persebacate, 4-nitrocumyl perpropionate, 1-phenylethylperbenzoate, phenylethyl nitro-perbenzoate,t-butylbicyclo-(2,2,1)heptane percarboxylate, t-butyl-4-carbomethoxyperbutyrate, t-butylcyclobutane percarboxylate, t-butylcyclohexylperoxycarboxylate, t-butylcyclopentyl percarboxylate,t-butylcyclopropane percarboxylate, t-butyldimethyl percinnamate,t-butyl-2-(2,2-diphenylvinyl) perbenzoate, t-butyl-4-methoxyperbenzoate, t-butylperbenzoate, t-butylcarboxycyclohexane, t-butylpernaphthoate, t-butyl peroxyisopropylcarbonate, t-butyl pertoluate,t-butyl-1-phenylcyclopropyl percarboxylate,t-butyl-2-propylperpentene-2-oate, t-butyl-1-methylcyclopropylpercarboxylate, t-butyl-4-nitrophenyl peracetate, t-butylnitrophenylperoxycarbamate, t-butyl-N-succiimido percarboxylate, t-butylpercrotonate, t-butyl permaleic acid, t-butyl permethacrylate, t-butylperoctoate, t-butyl peroxyisopropylcarbonate, t-butyl perisobutyrate,t-butyl peracrylate and/or t-butyl perpropionate.

Also contemplated are mixtures of these above listed freeradical-forming agents.

According to step c) of the instant process bifunctionally unsaturatedmonomer(s) and/or multifunctionally unsaturated low molecular weightpolymer(s) are provided.

“Bifunctionally unsaturated or multifunctionally unsaturated” as used inthe present application means preferably the presence of two or morenon-aromatic double bonds, as in e.g. divinylbenzene or cyclopentadieneor polybutadiene. Only such bi- or multifunctionally unsaturatedcompounds are used which can be polymerized preferably with the aid offree radicals. The unsaturated sites in the bi- or multifunctionallyunsaturated compounds are in their chemically bound state not actually“unsaturated”, because the double bonds are each used for a covalentbond to the polymer chains of the unmodified polypropylene.

Reaction of the bifunctionally unsaturated monomer(s) and/ormultifunctionally unsaturated low molecular weight polymer(s),preferably having a number average molecular weight (M_(n))<10000 g/mol,synthesized from one and/or more unsaturated monomers with thepolypropylene (PP), preferably the linear polypropylene (l-PP′), may beperformed in the presence of the thermally decomposing freeradical-forming agent.

In one embodiment, the bifunctionally unsaturated monomer(s) of step c)is/are selected from the group consisting of divinyl compounds, allylcompounds and dienes.

For example, the bifunctionally unsaturated monomers may be

-   -   divinyl compounds, such as divinylaniline, m-divinylbenzene,        p-divinylbenzene, divinylpentane and divinylpropane;    -   allyl compounds, such as allyl acrylate, allyl methacrylate,        allyl methyl maleate and allyl vinyl ether;    -   dienes, such as 1,3-butadiene, chloroprene, cyclohexadiene,        cyclopentadiene, 2,3-dimethylbutadiene, heptadiene, hexadiene,        isoprene and 1,4-pentadiene;    -   aromatic and/or aliphatic bis (maleimide) bis (citraconimide)        and mixtures of these unsaturated monomers.

Especially preferred bifunctionally unsaturated monomers are1,3-butadiene, isoprene, dimethyl butadiene and divinylbenzene.

The multifunctionally unsaturated low molecular weight polymer,preferably having a number average molecular weight (M_(n))<10000 g/molmay be synthesized from one or more unsaturated monomers.

Examples of such low molecular weight polymers are

-   -   polybutadienes, especially where the different microstructures        in the polymer chain, i.e. 1,4-cis, 1,4-trans and 1,2-(vinyl)        are predominantly in the 1,2-(vinyl) configuration    -   copolymers of butadiene and styrene having 1,2-(vinyl) in the        polymer chain.

A preferred low molecular weight polymer is polybutadiene, in particulara polybutadiene having more than 50.0 wt.-% of the butadiene in the1,2-(vinyl) configuration.

The branched polypropylene (b-PP), preferably the high melt strengthpolypropylene (HMS-PP), may contain more than one bifunctionallyunsaturated monomer and/or multifunctionally unsaturated low molecularweight polymer. Even more preferred the amount of bifunctionallyunsaturated monomer(s) and multifunctionally unsaturated low molecularweight polymer(s) together in the branched polypropylene (b-PP),preferably the high melt strength polypropylene (HMS-PP), is from 0.01to 10.0 wt.-%, based on said branched polypropylene (b-PP), preferablythe high melt strength polypropylene (HMS-PP).

According to step d) of the instant process a linear polypropylene(l-PP) is provided.

During the preparation of the instant polypropylene composition a linearpolypropylene (1-PP) is added. One specific finding of the presentinvention is that the introduction of the linear polypropylene (l-PP) isdecisive for preparing the specific polypropylene composition comprisinga branched polypropylene (b-PP) in a single step process, i.e. without asubsequent process step in which the obtained product is furthervis-broken to receive a polypropylene composition and/or branchedpolypropylene (b-PP) having the desired melt flow rate MFR₂ (230° C.)measured according to ISO 1133 in the range from 18.0 to 35.0 g/10 min.This linear polypropylene (l-PP) is further preferably used to bringadditives (A) in the instant polypropylene composition. It is a furtherfinding of the present invention that especially good results in view ofoptical properties, i.e. in terms of low OCS gel index, are achieved forthe instant polypropylene composition and/or branched polypropylene(b-PP) if the additives (A) are brought in by use of a specificpolypropylene carrier. Accordingly in a preferred embodiment theadditives (A) are introduced in the instant polypropylene composition inthe form of an additive mixture (AM), wherein said additive mixturecomprises, preferably consists of, the linear polypropylene (l-PP) andthe additives (A).

It is preferred that the linear polypropylene (l-PP) must have a ratherlow molecular weight and thus a rather high melt flow rate. Accordingly,it is required that the linear polypropylene (l-PP) has a melt flow rateMFR₂ (230° C.) measured according to ISO 1133 in the range from 10.0 to50.0 g/10 min, preferably in the range from 20.0 to 40.0 g/10 min, likein the range from 25.0 to 38.0 g/10 min. For example, the linearpolypropylene (l-PP) has a melt flow rate MFR₂ (230° C.) measuredaccording to ISO 1133 in the range from 28.0 to 38.0 g/10 min,preferably in the range from 30.0 to 38.0 g/10 min and most preferablyin the range from 32.0 to 38.0 g/10 min.

Preferably, the linear polypropylene (l-PP) has a melting point of atleast 140° C., more preferably of at least 150° C., still morepreferably of at least 160° C. and most preferably of at least 170° C.

Furthermore, as mentioned above the linear polypropylene (l-PP) shows noor nearby no-branching structure. Due to the absence of branches thelinear polypropylene (l-PP) is preferably featured by a low v₃₀ meltextensibility and/or a low F₃₀ melt strength.

Thus it is preferred that the linear polypropylene (l-PP) has

-   a v₃₀ melt extensibility of below 200 mm/s, preferably of below 190    mm/s, more preferably in the range of 100 to below 200 mm/s, still    more preferably in the range of 120 to 190 mm/s, yet more preferably    in the range of 120 to 175 mm/s, like in the range of 125 to 170    mm/s.

Accordingly, in one specific embodiment the linear polypropylene (l-PP)has

-   (a) a melt flow rate MFR₂ (230° C.) measured according to ISO 1133    in the range from 10.0 to 50.0 g/10 min, preferably in the range    from 20.0 to 40.0 g/10 min, like in the range from 25.0 to 38.0 g/10    min, more preferably in the range from 28.0 to 38.0 g/10 min, still    more preferably in the range from 30.0 to 38.0 g/10 min, yet more    preferably in the range from 32.0 to 38.0 g/10 min; and-   (b) a v₃₀ melt extensibility of below 200 mm/s, preferably of below    190 mm/s, more preferably in the range of 100 to below 200 mm/s,    still more preferably in the range of 120 to 190 mm/s, yet more    preferably in the range of 120 to 175 mm/s, like in the range of 125    to 170 mm/s.

Therefore, in one specific embodiment the linear polypropylene (l-PP)has a melt flow rate MFR₂ (230° C.) in the range from 10.0 to 50.0 g/10min and a v₃₀ melt extensibility of below 200 mm/s, preferably a meltflow rate MFR₂ (230° C.) in the range from 20.0 to 40.0 g/10 min and av₃₀ melt extensibility of below 190 mm/s, more preferably a melt flowrate MFR₂ (230° C.) like in the range from 25.0 to 38.0 g/10 min and av₃₀ melt extensibility in the range of 100 to below 200 mm/s, yet morepreferably a melt flow rate MFR₂ (230° C.) in the range from 28.0 to38.0 g/10 min and in the range of 120 to 190 mm/s, still yet morepreferably a melt flow rate MFR₂ (230° C.) in the range from 30.0 to38.0 g/10 min and in the range of 120 to 175 mm/s, like a melt flow rateMFR₂ (230° C.) in the range from 32.0 to 38.0 g/10 min and a v₃₀ meltextensibility in the range of 125 to 170 mm/s.

In one embodiment of the present invention, the linear polypropylene(l-PP) has a F₃₀ melt strength of more than 1.0 cN, preferably of morethan 2.0 cN, more preferably in the range of 1.0 to 65 cN, still morepreferably in the range of 1.5 to 50 cN, yet more preferably in therange of 2.0 to 50 cN, still yet more preferably in the range of 2.5 to50 cN like in the range of 2.5 to 30 cN.

The linear polypropylene (l-PP) can be produced in a known manner forinstance by employing a single-site or a Ziegler Natta catalyst. Thelinear polypropylene (l-PP) can be a propylene homopolymer (H-PP),preferably a linear propylene homopolymer (1-H-PP), or a propylenecopolymer (R-PP), preferably a linear propylene copolymer (1-R-PP).Concerning the comonomer content and type of comonomer it is referred tothe information provided above for the branched polypropylene (b-PP)especially it is referred to the high melt strength random propylenecopolymer (R-HMS-PP). Preferably, the linear polypropylene (1-PP) is alinear propylene homopolymer (1-H-PP). Accordingly all informationprovided with regard to melt flow rate MFR₂ (230° C.), melting point,F₃₀ melt strength, v₃₀ melt extensibility, and particle size andparticle size distribution, respectively, applies especially for thelinear propylene homopolymer (1-H-PP).

In a specific embodiment the polypropylene (PP), preferably the linearpolypropylene (1-PP′), and the linear polypropylene (l-PP) are linearpropylene homopolymers, i.e. a linear propylene homopolymer (1-H-PP) anda linear propylene homopolymer (1-H-PP′). It is preferred that thelinear propylene homopolymers, i.e. the linear propylene homopolymer(1-H-PP) and the linear propylene homopolymer (1-H-PP′), have differingproperties, in particular in view of the melt flow rate MFR₂ (230° C.).

As mentioned above the linear polypropylene (l-PP) is used as a carrierto introduce the optional at least one additive (A) in the polypropylenecomposition. In other words an additive mixture (AM) comprising,preferably consisting of, the linear polypropylene (l-PP) and the atleast one additive (A) is used in the instant process for themanufacture of the polypropylene composition.

It is thus preferred that the linear polypropylene (l-PP) comprises atleast one additive (A). For example, the linear polypropylene (l-PP)comprises two or three additives (A), like two additives (A).

The at least one additives (A) can be any additive useful in thetechnical area of the high melt strength polypropylene (HMS-PP) and itsapplications.

For example, the at least one additives (A) to be used in the linearpolypropylene (l-PP) and thus in form of the additive mixture (AM)include, but are not limited to, stabilizers such as antioxidants (e.g.sterically hindered phenols, phosphites/phosphonites, sulphur containingantioxidants, alkyl radikal scavangers, aromatic amines, hindered aminestabilizers, or blends thereof), metal deactivators (e.g. Irganox MD1024), or UV stabilizers (e.g. hindered amine light stabilizers). Othertypical additives are modifiers such as antistatic or antifogging agents(e.g. ethoxylated amines and amides, or glycerol esters), acidscavengers (e.g. Ca-stearate), blowing agents, cling agents (e.g.polyisobutene), lubricants and resins (ionomer waxes, PE- and ethylenecopolymer waxes, Fischer-Tropsch waxes, Montan-based waxes, Fluoro-basedcompounds, or paraffin waxes), nucleating agents (e.g. talc, benzoates,phosphorous-based compounds, sorbitoles, nonitol-based compounds, oramide-based compounds), as well as slip and antiblocking agents (e.g.erucamide, oleamide, talc natural silica and synthetic silica, orzeolites). Preferably, the at least one additive (A) is selected fromthe group consisting of antioxidants (e.g. sterically hindered phenols,phosphites/phosphonites, sulphur containing antioxidants, alkyl radikylscavangers, aromatic amines, hindered amine stabilizers, or blendsthereof), metal deactivators (e.g. Irganox MD 1024), or UV stabilizers(e.g. hindered amine light stabilizers), antistatic or antifoggingagents (e.g. ethoxylated amines and amides, or glycerol esters), acidscavengers (e.g. Ca-stearate), blowing agents, cling agents (e.g.polyisobutene), lubriciants and resins (ionomer waxes, PE- and ethylenecopolymer waxes, Fischer-Tropsch waxes, Montan-based waxes, Fluoro-basedcompounds, or paraffin waxes), nucleating agents (e.g. talc, benzoates,phosphorous-based compounds, sorbitoles, nonitol-based compounds, oramide-based compounds), slip agents, antiblocking agents (e.g.erucamide, oleamide, talc natural silica and synthetic silica, orzeolites) and mixtures thereof.

Typically the total amount of the at least one additive (A) in theadditive mixture (AM) is not more than 25.0 wt.-%, more preferably notmore than 20.0 wt.-%, like in the range of 5.0 to 20.0 wt.-% based onthe total weight of the additive mixture (AM). For example, the totalamount of the at least one additive (A) in the additive mixture (AM) isin the range of 10.0 to 20.0 wt.-% based on the total weight of theadditive mixture (AM).

According to steps e) and f) of the instant process the polypropylene(PP), preferably the linear polypropylene (l-PP′), of step a) is reactedwith the thermally decomposing free radical-forming agent of step b) andthe bifunctionally unsaturated monomer(s) and/or with multifunctionallyunsaturated low molecular weight polymer(s) of step c) obtaining therebythe branched polypropylene (b-PP) and, further, said branchedpolypropylene (b-PP) is reacted with the linear polypropylene (l-PP) ofstep d).

One essential aspect of the present invention is that the preparation ofthe instant polypropylene composition comprising the branchedpolypropylene (b-PP), i.e. the high melt strength polypropylene(HMS-PP), is carried out by using a polypropylene (PP), preferably thelinear polypropylene (l-PP′), having a melt flow rate MFR₂ (230° C.) ofmore than 1.0 g/10 min, a thermally decomposing free radical-formingagent, bifunctionally unsaturated monomer(s) and/or withmultifunctionally unsaturated low molecular weight polymer(s) and alinear polypropylene (l-PP) having a melt flow rate MFR₂ (230° C.) of10.0 to 50.0 g/10 min.

Accordingly, the present invention relates to a process for providing apolypropylene composition comprising the branched polypropylene (b-PP),wherein the process comprises step e) in which the polypropylene (PP),preferably the linear polypropylene (l-PP′), of step a) is reacted withthe thermally decomposing free radical-forming agent of step b) and thebifunctionally unsaturated monomer(s) and/or with multifunctionallyunsaturated low molecular weight polymer(s) of step c) obtaining therebythe branched polypropylene (b-PP). The process further comprises step f)in which the branched polypropylene (b-PP) obtained in step e) isreacted with the linear polypropylene (l-PP) of step d) obtainingthereby the polypropylene composition. Concerning the definitions andpreferred embodiments of the branched polypropylene (b-PP), thepolypropylene (PP), preferably the linear polypropylene (l-PP′), thethermally decomposing free radical-forming agent, the bifunctionallyunsaturated monomer(s) and/or multifunctionally unsaturated lowmolecular weight polymer(s) and the linear polypropylene (l-PP),reference is made to the information provided above.

Preferably the instant process is a single step process, i.e. no furtherprocess steps are required subsequent to process steps e) and f). Inother words, the instant process allows obtaining a polypropylenecomposition comprising a branched polypropylene (b-PP) having a meltflow rate MFR₂ (230° C.) measured according to ISO 1133 in the rangefrom 18.0 to 35.0 g/10 min without implementing a subsequentvis-breaking step.

As mentioned above, in step e) the branched polypropylene (b-PP), i.e.the high melt strength polypropylene (HMS-PP), is obtained by treatingthe polypropylene (PP), preferably the linear polypropylene (l-PP′),with thermally decomposing radical-forming agents.

However in such a case a high risk exists that the polypropylene (PP),preferably the linear polypropylene (l-PP′), is degraded, which isdetrimental. Thus, it is preferred that the chemical modification isaccomplished by the additional use of bifunctionally unsaturatedmonomer(s) and/or multifunctionally unsaturated low molecular weightpolymer(s) as chemically bound bridging unit(s). A suitable method toobtain the branched polypropylene (b-PP), i.e. the high melt strengthpolypropylene (HMS-PP), is for instance disclosed in EP 0 787 750, EP 0879 830 A1 and EP 0 890 612 A2. All documents are herewith included byreference. Thereby, the amount of thermally decomposing radical-formingagents, preferably of peroxide, is preferably in the range of 0.05 to3.00 wt.-% based on the amount of the polypropylene (PP), preferably thelinear polypropylene (l-PP′). Typically, the thermally decomposingradical-forming agents are added together with the bifunctionallyunsaturated monomer(s) and/or with multifunctionally unsaturated lowmolecular weight polymer(s) to the polypropylene (PP), preferably to thelinear polypropylene (l-PP′).

However it is also possible, but less preferred, that first thebifunctionally unsaturated monomer(s) and/or multifunctionallyunsaturated low molecular weight polymer(s) is/are added to thepolypropylene (PP), preferably to the linear polypropylene (l-PP′), andsubsequent the thermally decomposing radical-forming agents, or theother way round, first the thermally decomposing radical-forming agentsare added to the polypropylene (PP), preferably to the linearpolypropylene (l-PP′), and subsequent the bifunctionally unsaturatedmonomer(s) and/or multifunctionally unsaturated low molecular weightpolymer(s).

Preferably step f) is initiated when at least 70%, preferably at least80%, yet more preferably at least 90%, like at least 95 or 99%, of thereaction between the polypropylene (PP), preferably the linearpolypropylene (l-PP′), and the thermally decomposing freeradical-forming agent and the bifunctionally unsaturated monomer(s)and/or multifunctionally unsaturated low molecular weight polymer(s) hastaken place to obtain the branched polypropylene (b-PP), i.e. the highmelt strength polypropylene (HMS-PP).

In a preferred embodiment, an extruder, such as a twin screw extruder,is used for steps e) and f).

The use of an extruder is particularly advantageous in that it cansimultaneously be used for the preparation of the branched polypropylene(b-PP), i.e. the high melt strength polypropylene (HMS-PP), and foradding the linear polypropylene (l-PP) or for adding the additivemixture (AM) to said branched polypropylene (b-PP). In a preferredembodiment, the polypropylene (PP), preferably the linear polypropylene(l-PP′), is added to an extruder together with—as described in detailabove—the thermally decomposing free radical-forming agent, preferably aperoxide, and the bifunctionally unsaturated monomer(s) and/or themultifunctionally unsaturated low molecular weight polymer(s),preferably with bifunctionally unsaturated monomer(s) selected fromdivinyl compounds, allyl compounds or dienes, to provide the branchedpolypropylene (b-PP), i.e. the high melt strength polypropylene(HMS-PP), in step e). It is also possible to use a combination of anextruder downstream a pre-mixing device, wherein the bifunctionallyunsaturated monomer(s) and/or multifunctionally unsaturated lowmolecular weight polymer(s) and the thermally decomposing freeradical-forming agent are added to the polypropylene (PP), preferablythe linear polypropylene (l-PP′), in the pre-mixing device.Subsequently, in a step f) the linear polypropylene (l-PP) or theadditive mixture (AM) based on said linear polypropylene (l-PP)comprising the at least one additive (A) is preferably added at thedownstream end of the extruder screw in order not to interfere with themodification reaction for providing branched polypropylene (b-PP), i.e.the high melt strength polypropylene (HMS-PP), as described above. Inthis respect, the term “downstream end of the extruder screw” isunderstood as within the last 60% of the length of the extruder screw,preferably within the last 65% of the length of the extruder screw, morepreferably at least 70% of the length of the extruder screw, like atleast 75% of the extruder screw.

The extruder (E) used for the instant process preferably comprises inoperation direction a first mixing zone (MZ1) and a second mixing zone(MZ2). For example, the extruder (E) used for the instant processpreferably comprises a feed-throat (FT), a first mixing zone (MZ1), asecond mixing zone (MZ2) and a die (D), wherein between the first mixingzone (MZ1) and the second mixing zone (MZ2) a side feed-throat (SFT) islocated. It is preferred that reacting step e) takes place in the firstmixing zone (MZ1) whereas reacting step f) takes place in the secondmixing zone (MZ2) of the extruder.

It is further preferred that not more than 10.0 wt.-% of the totalamount of the branched polypropylene (b-PP) of the polypropylenecomposition is produced in the second mixing zone (MZ2).

Preferably, the extruder is a screw extruder, like a twin screwextruder. Accordingly the polypropylene (PP), preferably the linearpolypropylene (l-PP′), the thermally decomposing free radical-formingagent, preferably a peroxide, and the bifunctionally unsaturatedmonomer(s) and/or multifunctionally unsaturated low molecular weightpolymer monomer(s), preferably selected from divinyl compounds, allylcompounds or dienes, but not the linear polypropylene (l-PP), and notthe additives (A), are fed via the feed-throat (FT), thereby preferablyusing a feeder, into the extruder and is/are subsequently passeddownstream through the first mixing zone (MZ1).

Preferably the shear stress in said first mixing zone (MZ1) is of suchextent that the polypropylene (PP), preferably the linear polypropylene(l-PP′), is molten and the chemical reaction with the thermallydecomposing free radical-forming agent and the bifunctionallyunsaturated monomer(s) and/or multifunctionally unsaturated lowmolecular weight polymer(s) is initiated. After the first mixing zone(MZ1), i.e. between the first mixing zone (MZ1) and the second mixingzone (MZ2), the linear polypropylene (l-PP), or the additive mixture(AM) is added, i.e. fed into the extruder. Preferably, the linearpolypropylene (l-PP), or the additive mixture (AM) is added via the sidefeed-throat (SFT), thereby preferably using a side feeder. Subsequently,all components of the polypropylene composition, including the linearpolypropylene (l-PP), or the additive mixture (AM) are passed downstreamthrough the second mixing zone (MZ2). Finally the polypropylenecomposition comprising the branched polypropylene (b-PP) is dischargedvia the die (D).

Preferably, the first mixing zone (MZ1) is longer than the second mixingzone (MZ2). Preferably the length ratio between the first mixing zone(MZ1) to the second mixing zone (MZ2) [mm (MZ1)/mm (MZ2)] is at least2/1, more preferably 3/1, yet more preferably in the range of 2/1 to15/1, still more preferably 3/1 to 10/1.

It is preferred that 1.0 to 6.0 parts by weight of the linearpolypropylene (l-PP) are added to 94.0 to 99.0 parts by weight ofbranched polypropylene (b-PP), based on the total weight of thepolypropylene composition. In one embodiment of the present invention,1.0 to 3.0 parts by weight of the linear polypropylene (l-PP) are addedto 97.0 to 99.0 parts by weight of branched polypropylene (b-PP), basedon the total weight of the polypropylene composition. For example, 2.0parts by weight of the linear polypropylene (l-PP) are added to 98.0parts by weight of branched polypropylene (b-PP), based on the totalweight of the polypropylene composition.

As mentioned above due to the instant process a polypropylenecomposition is obtained which comprises a branched polypropylene (b-PP),i.e. a high melt strength polypropylene (HMS-PP). In a preferredembodiment, the instant polypropylene composition comprises, preferablyconsists of, a branched polypropylene (b-PP), i.e. a high melt strengthpolypropylene (HMS-PP), a polypropylene (PP), preferably a linearpolypropylene (l-PP′), a linear polypropylene (l-PP) and optionally atleast one additive (A).

The major component in the instant polypropylene composition is thebranched polypropylene (b-PP), i.e. the high melt strength polypropylene(HMS-PP). Accordingly the polypropylene composition comprises at least70 wt.-%, more preferably at least 75 wt.-%, yet more preferably atleast 80 wt.-%, still more preferably at least 85 wt.-%, still yet morepreferably at least 90 wt.-%, like at least 95 wt.-%, of the branchedpolypropylene (b-PP), i.e. the high melt strength polypropylene(HMS-PP), based on the total weight of the polypropylene composition.

In one embodiment of the present invention, the instant polypropylenecomposition comprises

-   (a) 80.0 to 99.0 parts by weight, preferably 90.0 to 99.0 parts by    weight, more preferably 95.0 to 99.0 parts by weight, of the    branched polypropylene (b-PP), preferably of the high melt strength    polypropylene (HMS-PP); and-   (b) 1.0 to 20.0 parts by weight, preferably 1.0 to 10.0 parts by    weight, more preferably 1.0 to 5.0 parts by weight, of the linear    polypropylene (l-PP), based on the total weight of the polypropylene    composition.

In a preferred embodiment the branched polypropylene (b-PP), i.e. thehigh melt strength polypropylene (HMS-PP), and the linear polypropylene(l-PP), are the only polymer components in the polypropylenecomposition. In other words the polypropylene composition may comprisefurther at least one additive (A) as defined in more detail above but noother polymers in an amount exceeding 5.0 wt.-%, more preferablyexceeding 2.0 wt.-%, still more preferably exceeding 1.0 wt.-%, based onthe total weight of the polypropylene composition. In a specificembodiment of the present invention, the polypropylene compositionconsists of the branched polypropylene (b-PP), i.e. the high meltstrength polypropylene (HMS-PP), the linear polypropylene (l-PP), and atleast one additive (A).

Preferably the total amount of additives (A) in the polypropylenecomposition is not more than 5.0 wt.-%, more preferably not more than1.0 wt.-%, like in the range of 0.005 to 0.5 wt.-%, based on the totalweight of the polypropylene composition.

Therefore, the present process is directed to the manufacture of apolypropylene composition comprising

-   (a) 80.0 to 99.0 parts by weight, preferably 90.0 to 99.0 parts by    weight, more preferably 95.0 to 99.0 parts by weight, of the    branched polypropylene (b-PP), i.e. of the high melt strength    polypropylene (HMS-PP);-   (b) 1.0 to 20.0 parts by weight, preferably 1.0 to 10.0 parts by    weight, more preferably 1.0 to 5.0 parts by weight, of the linear    polypropylene (l-PP), having a melt flow rate MFR₂ (230° C.)    measured according to ISO 1133 in the range from 10.0 to 50.0 g/10    min, preferably in the range from 20.0 to 40.0 g/10 min, more    preferably in the range from 25.0 to 38.0 g/10 min, yet more    preferably in the range from 28.0 to 38.0 g/10 min, like in the    range from 30.0 to 38.0 g/10 min or in the range from 32.0 to 38.0    g/10 min; and-   (c) optionally 0.005 to 5.0, preferably 0.005 to 2.0, more    preferably 0.05 to 1.0, like 0.05 to 0.5, parts by weight of at    least one additive (A), preferable two additives (A), wherein said    at least one additive (A) is preferably selected from the group    consisting of antioxidants, metal deactivators, UV-stabilizers,    antistatic agents, antifogging agents, acid scavengers, blowing    agents, cling agents, lubricants, nucleating agents, slip agents,    antiblocking agents and mixtures thereof.

As mentioned above, the branched polypropylene (b-PP), i.e the high meltstrength polypropylene (HMS-PP), is the dominant part in the instantpolypropylene composition. Accordingly it is preferred that the finalpolypropylene composition shows a similar rheology behavior as thebranched polypropylene (b-PP), i.e. the high melt strength polypropylene(HMS-PP).

Thus, the instant polypropylene composition preferably has a F₃₀ meltstrength of more than 3.4 cN and a v₃₀ melt extensibility of more than200 mm/s, more preferably a F₃₀ melt strength from 4.0 to 20.0 cN and av₃₀ melt extensibility from 240 to 300 mm/s and most preferably a F₃₀melt strength from 4.0 to 10.0 cN and a v₃₀ melt extensibility from 240to 300 mm/s, wherein the F₃₀ melt strength and the v₃₀ meltextensibility are measured according to ISO 16790:2005,

Additonally or alternatively, the instant polypropylene compositionpreferably has a melt flow rate MFR₂ (230° C.) measured according to ISO1133 of 18.0 to 35.0 g/10 min, more preferably from 19.0 to 30.0 g/10min and most preferably from 19.0 to 25.0 g/10 min

Additonally or alternatively, the instant polypropylene compositionpreferably has an OCS gel index of less than 2,500, preferably of lessthan 2,000 and most preferably from 500 to 2,000.

Hence, in one specific embodiment of the present invention, the instantpolypropylene composition preferably has

-   -   a) a F₃₀ melt strength of more than 3.4 cN and a v₃₀ melt        extensibility of more than 200 mm/s, preferably a F₃₀ melt        strength from 4.0 to 20.0 cN and a v₃₀ melt extensibility from        240 to 300 mm/s and most preferably a F₃₀ melt strength from 4.0        to 10.0 cN and a v₃₀ melt extensibility from 240 to 300 mm/s,        wherein the F₃₀ melt strength and the v₃₀ melt extensibility are        measured according to ISO 16790:2005,    -   and    -   b) a melt flow rate MFR₂ (230° C.) measured according to ISO        1133 of 18.0 to 35.0 g/10 min, preferably from 19.0 to 30.0 g/10        min and most preferably from 19.0 to 25.0 g/10 min, and    -   c) an OCS gel index of less than 2,500, preferably of less than        2,000 and most preferably from 500 to 2,000.

One essential finding of the present invention is that the instantpolypropylene composition and thus films made from said polypropylenecomposition (especially as defined below) show a reduced OCS gel index.Accordingly it is preferred that the instant polypropylene compositionhas an OCS gel index of less than 2,500, preferably of less than 2,000and most preferably from 500 to 2,000.

Keeping the information provided above in mind the present inventioncovers a polypropylene composition comprising

-   -   (a) 95.0 to 99.0 parts by weight of a branched polypropylene        (b-PP); and    -   (b) 1.0 to 5.0 parts by weight of a linear polypropylene (l-PP)        having a melt flow rate MFR₂ (230° C.) measured according to ISO        1133 of 10.0 to 50.0 g/10 min, preferably from 20.0 to 40.0 g/10        min;    -   wherein the polypropylene composition has        -   a melt flow rate MFR₂ (230° C.) measured according to ISO            1133 from 18.0 to 35.0 g/10 min, and        -   an OCS gel index of less than 2,500; and    -   wherein the polypropylene composition and/or the branched        polypropylene (b-PP) has/have a F₃₀ melt strength of more than        3.4 cN and a v₃₀ melt extensibility of more than 200 mm/s,        wherein the F₃₀ melt strength and the v₃₀ melt extensibility are        measured according to ISO 16790:2005.

For example, the polypropylene composition comprises

-   -   (a) 95.0 to 99.0 parts by weight of a branched polypropylene        (b-PP); and    -   (b) 1.0 to 5.0 parts by weight of a linear polypropylene (l-PP)        having a melt flow rate MFR₂ (230° C.) measured according to ISO        1133 from 25.0 to 38.0 g/10 min;    -   wherein the polypropylene composition has        -   a melt flow rate MFR₂ (230° C.) measured according to ISO            1133 from 19.0 to 25.0 g/10 min, and        -   an OCS gel index of less than 2,000;    -   and wherein further the polypropylene composition and/or the        branched polypropylene (b-PP) has/have a F₃₀ melt strength from        4.0 to 20.0 cN and a v₃₀ melt extensibility from 240 to 300        mm/s, wherein the F₃₀ melt strength and the v₃₀ melt        extensibility are measured according to ISO 16790:2005.

As mentioned above, the present invention also features a filmcomprising the instant polypropylene composition described herein.Preferably the film is a cast film or a blown film. The film may also bea biaxially oriented film, like biaxially oriented blown film. Thedifferences between such films are known to the skilled person.Reference is made in this regard to the “Polypropylene Handbook”, pages405 to 414, 2^(nd) Edition, Nello Pasquini (Ed.), Hanser. Preferably thefilm comprises at least 70 wt.-%, more preferably at least 80 wt.-%,more preferably at least 90 wt.-%, yet more preferably at least 95wt.-%, of the polypropylene composition according to the instantinvention. In a preferred embodiment the film consists of the instantpolypropylene composition.

The preparation of the films is accomplished by methods known in theart. For instance, the film can be produced by cast film or blown filmtechnology. In the cast film technology the molten polypropylenecomposition is extruded through a slot extrusion die onto a chill rollto cool the polymer to a solid film. Typically the polypropylenecomposition is firstly compressed and liquefied in an extruder, it beingpossible for any additives to be already added to the polymer orintroduced at this stage via a masterbatch. The melt is then forcedthrough a flat-film die (slot die), and the extruded film is taken offon one or more take-off rolls, during which it cools and solidifies. Ithas proven particularly favorable to keep the take-off roll or rolls, bymeans of which the extruded film is cooled and solidified, at atemperature from 10 to 50° C., preferably from 10 to 40° C., morepreferably from 12 to 35° C. The obtained product is an unstretched filmwhich can if desired biaxially stretched.

In the blown film process the polypropylene composition is extrudedthrough an annular die and blown into a tubular film by forming a bubblewhich is collapsed between nip rollers after solidification. The blownextrusion can be preferably effected at a temperature in the range 160to 240° C., and cooled by water or preferably by blowing gas (generallyair) at a temperature of 10 to 50° C. to provide a frost line height of0.5 to 8 times the diameter of the die. The blow up ratio shouldgenerally be in the range of from 1.5 to 4, such as from 2 to 4,preferably 2.5 to 3.5.

In the following, the present invention is described in more detail byway of examples.

EXAMPLES A. Measuring Methods

The following definitions of terms and determination methods apply forthe above general description of the invention as well as to the belowexamples unless otherwise defined.

Comonomer Content in Polypropylene

The comonomer content is determined by quantitative Fourier transforminfrared spectroscopy (FTIR) after basic assignment calibrated viaquantitative ¹³C nuclear magnetic resonance (NMR) spectroscopy in amanner well known in the art. Thin films are pressed to a thickness of250 μm and spectra recorded in transmission mode.

Specifically, the ethylene content of a polypropylene-co-ethylenecopolymer is determined using the baseline corrected peak area of thequantitative bands found at 720-722 and 730-733 cm′.Propylene-1-butene-copolymers were evaluated at 767 cm′. Quantitativeresults are obtained based upon reference to the film thickness.

Melting Temperature (T_(m)) and Heat of Fusion (H_(f)), CrystallizationTemperature (T_(c)) and Heat of Crystallization (H_(c)):

measured with Mettler TA820 differential scanning calorimetry (DSC) on 5to 10 mg samples. DSC is run according to ISO 3146/part 3/method C2 in aheat/cool/heat cycle with a scan rate of 10° C./min in the temperaturerange of +23 to +210° C. Crystallization temperature and heat ofcrystallization (H_(c)) are determined from the cooling step, whilemelting temperature and heat of fusion (H_(f)) are determined from thesecond heating step

MFR₂ (230° C.) is measured according to ISO 1133 (230° C., 2.16 kgload).

F₃₀ Melt Strength and v₃₀ Melt Extensibility

The test described herein follows ISO 16790:2005.

The strain hardening behaviour is determined by the method as describedin the article “Rheotens-Mastercurves and Drawability of Polymer Melts”,M. H. Wagner, Polymer Engineering and Science, Vol. 36, pages 925 to935. The content of the document is included by reference. The strainhardening behaviour of polymers is analysed by Rheotens apparatus(product of Gottfert, Siemensstr.2, 74711 Buchen, Germany) in which amelt strand is elongated by drawing down with a defined acceleration.

The Rheotens experiment simulates industrial spinning and extrusionprocesses. In principle a melt is pressed or extruded through a rounddie and the resulting strand is hauled off. The stress on the extrudateis recorded, as a function of melt properties and measuring parameters(especially the ratio between output and haul-off speed, practically ameasure for the extension rate). For the results presented below, thematerials were extruded with a lab extruder HAAKE Polylab system and agear pump with cylindrical die (L/D=6.0/2.0 mm). The gear pump waspre-adjusted to a strand extrusion rate of 5 mm/s, and the melttemperature was set to 200° C. The spinline length between die andRheotens wheels was 80 mm. At the beginning of the experiment, thetake-up speed of the Rheotens wheels was adjusted to the velocity of theextruded polymer strand (tensile force zero): Then the experiment wasstarted by slowly increasing the take-up speed of the Rheotens wheelsuntil the polymer filament breaks. The acceleration of the wheels wassmall enough so that the tensile force was measured under quasi-steadyconditions. The acceleration of the melt strand drawn down is 120mm/sec². The Rheotens was operated in combination with the PC programEXTENS. This is a real-time data-acquisition program, which displays andstores the measured data of tensile force and drawdown speed. The endpoints of the Rheotens curve (force versus pulley rotary speed) is takenas the F₃₀ melt strength and drawability values.

OCS Gel Index

1. Apparatus

The apparatus consists of a laboratory extruder ME 25/5200 V1 with threeheating zones, an adapter and a 150 mm broad die. The follow-on unitencompasses a chillroll CR-8, diameter 140 mm, including Haake C40Pheating- and cooling device (15 to 90° C.), a line scan camera FS-5/4096Pixel (dynamical digital converting of gray scale images) and a wind-upunit with automatic tension control up to 10 N.

2. Material-Specific Settings for Film-Manufacturing

The temperature setting for the heating zones at cylinder and die isclassified for polypropylene according to MFR-ranges in three groups:

-   Group 1: MFR-range 0.3-2.0 g/10 min (230° C./2.16 kg), temperatures    220/260/270/280/290° C.-   Group 2: MFR-range 2.0-10 g/10 min (230° C./2.16 kg), temperatures    220/230/240/250/260° C.-   Group 3: MFR-range 10-33 g/10 min (230° C./2.16 kg), temperatures    200/220/230/240/240° C.

Preset Parameters:

Rotational speed (screw): 30 rpm

Haul-off speed: 3 m/min;

The film thickness is 50 μm

3. Measurement

After fulfilment of the following parameters: In case of similarmaterials ca. 60 min running-in period, in case of highly divergingmaterials ca. 120 min.

Goal:

Adjustment of a homogenous film at constant melt pressure and melttemperature. The measuring area is standardised at 5 m². The measurementitself is terminated automatically when the area is accomplished. Thereport will be printed simultaneously.

4. Analysis

The number of found defects is, referring 1/m², class-divided accordingto size and multiplied with the mass factor, adding up to the gelindex.

Size class 1 100-300 μm mass factor × 0.1 Size class 2 301-600 μm massfactor × 1.0 Size class 3 601-1000 μm mass factor × 5.0 Size class4 >1000 μm mass factor × 10

Example

17 defects  size class 1 ×0.1 = 1.7 5 defects size class 2 × 1.0 =5.0 2defects size class 3 × 5.0 =10.0 0 defects size class 4 × 10.0 =0gelindex = 16.7

B. Examples Linear Polypropylenes (l-PP)

l-PP1 is a linear propylene homopolymer having a MFR₂ (230° C.) of 3.48g/10 min, a melting temperature Tm of 160° C., a F₃₀ melt strength of6.5 cN and v₃₀ melt extensibility 160 mm/s.

l-PP2 is a linear propylene homopolymer having a MFR₂ (230° C.) of 35g/10 min, a melting temperature Tm of 210-250° C. and v₃₀ meltextensibility 160 mm/s.

Additive Mixtures

The linear polypropylene l-PP2 was used to provide an additive mixturecontaining further additives as a masterbatch for incorporating into abase polymer of branched polypropylene.

The additive mixture contains 87.50 wt.-% of the respective linearpolypropylene l-PP2, 10.00 wt.-% Irganox B 225 FF (antioxidant), and2.50 wt.-% Hydrotalcit, based on the total weight of the additivemixture.

Inventive Examples IE1 to IE 4 and Comparative Example CE1

l-PP1 was subjected to a reactive extrusion in the presence of butadieneand peroxide as described in the following. Both the butadiene and theperoxide (amounts are indicated in table 1) were pre-mixed with thel-PP1 powder prior to the melt-mixing step in a horizontal mixer withpaddle stirrer at a temperature of 65° C., maintaining an averageresidence time of 15 to 20 minutes. The pre-mixture was transferredunder inert atmosphere to a co-rotating twin screw extruder of the typeTheyson TSK60 having a barrel diameter of 60 mm and an L/D-ratio of 48equipped with a high intensity mixing screw having 3 kneading zones anda two-step degassing setup. The temperature in the extruder was set to240° C. The screw speed and throughput is indicated in table 1. In thefirst ¾ of the extruder length the branched polypropylene is produced(b-PP). Subsequently, via a side feeder, i.e. at the last ¼ of theextruder length, the additive mixture as defined above is fed into theextruder to the produced branched polypropylene (b-PP). The extrudedpolypropylene composition was discharged and pelletized. From thepellets films have been produced as described above (OCS gel index). Theproperties of the pelletized polypropylene composition as well as of thefilms are indicated in table 2.

TABLE 1 Process conditions IE 1 IE 2 IE 3 IE 4 Peroxide* [wt.-%] 0.450.53 0.60 0.68 butadiene* [l/h] 130 80 65 65 screw speed [rpm] 400 400400 400 throughput [kg/h] 200 200 200 200 additive mixture* [wt.-%] 2 22 2 *based on the total weight of the polypropylene composition

TABLE 2 Properties of polypropylene composition and films OCS MFR₂ F₃₀STD v₃₀ STD gel index [g/10 min] [cN] F₃₀ [mm/s] v₃₀ [—] IE1 21.1 8.100.1 282 8 1980 IE2 19.7 8.20 0.1 273 4 744 IE3 22 4.50 0.1 287 11 745IE4 32.2 3.50 0.1 292 10 590 CE1 21.7 3.40 0.1 255 10 12434

A suitable polypropylene composition having a melt flow rate MFR₂ (230°C.) measured according to ISO 1133 of 18.0 to 35.0 g/10 min can beprepared in a single step process by incorporating a linearpolypropylene into a branched polypropylene, i.e. without implementing afurther vis-breaking step subsequent to the instant process. At the sametime, it can be gathered that the resulting polypropylene compositionexhibits higher melt strength F₃₀ as well as higher melt extensibilityv₃₀ compared to the reference material CE1 (commercially available asWF420HMS from Borealis AG, Austria). In addition thereto, the resultingpolypropylene composition shows a higher film quality expressed by lowervalues for the OCS gel index compared to the reference material CE1.

1. Process for providing a polypropylene composition comprising abranched polypropylene (b-PP), the process comprising the steps of: a)providing a polypropylene (PP) having a melt flow rate MFR₂ (230° C.) ofmore than 1.0 g/10 min; b) providing a thermally decomposing freeradical-forming agent, c) providing bifunctionally unsaturatedmonomer(s) and/or multifunctionally unsaturated low molecular weightpolymer(s), d) providing a linear polypropylene (l-PP) having a meltflow rate MFR₂ (230° C.) of 10.0 to 50.0 g/10 min, e) reacting thepolypropylene (PP) of step a) with the thermally decomposing freeradical-forming agent of step b) and the bifunctionally unsaturatedmonomer(s) and/or multifunctionally unsaturated low molecular weightpolymer(s) of step c) obtaining thereby the branched polypropylene(b-PP), and f) reacting the branched polypropylene (b-PP) obtained instep e) with the linear polypropylene (l-PP) of step d), wherein thepolypropylene composition and/or branched polypropylene (b-PP) has/havei) a melt flow rate MFR₂ (230° C.) measured according to ISO 1133 of18.0 to 35.0 g/10 min, ii) a F₃₀ melt strength of more than 3.4 cN and av₃₀ melt extensibility of more than 200 mm/s, wherein the F₃₀ meltstrength and the v₃₀ melt extensibility are measured according to ISO16790:2005.
 2. The process according to claim 1, wherein thepolypropylene (PP) has a melt flow rate MFR₂ (230° C.) measuredaccording to ISO 1133 in the range from 1.0 to 18.0 g/10 min.
 3. Theprocess according to claim 1, wherein the polypropylene (PP) (a) is alinear polypropylene (l-PP′); and/or (b) is a linear polypropylene(l-PP′) having a F₃₀ melt strength of more than 1.0 cN and a v₃₀ meltextensibility of below 200 mm/s, wherein the F₃₀ melt strength and thev₃₀ melt extensibility are measured according to ISO 16790:2005.
 4. Theprocess according to claims 1, wherein (a) the thermally decomposingfree radical-forming agent of step b) is a peroxide and/or (b) thebifunctionally unsaturated monomer(s) and/or multifunctionallyunsaturated low molecular weight polymer(s) of step c) is/are selectedfrom the group consisting of divinyl compounds, allyl compounds anddienes.
 5. The process according to anyone of the claim 1, wherein (a)the linear polypropylene (l-PP) of step d) has a melt flow rate MFR₂(230° C.) measured according to ISO 1133 from 20.0 to 40.0 g/10 minand/or (b) the linear polypropylene (l-PP) of step d) comprises at leastone additive (A) selected from the group consisting of antioxidants,metal deactivators, UV-stabilizers, antistatic agents, antifoggingagents, acid scavengers, blowing agents, cling agents, lubricants,nucleating agents, slip agents, antiblocking agents and mixturesthereof, and/or (c) the branched polypropylene (b-PP) obtained in stepe) is free of additives (A).
 6. The process according to claim 1,wherein steps e) and f) are accomplished in an extruder, said extrudercomprises in operation direction a first mixing zone (MZ1) and a secondmixing zone (MZ2), wherein further step e) takes place in the firstmixing zone (MZ1) whereas step f) takes place in the second mixing zone(MZ2).
 7. The process according to claim 6, wherein the extrudercomprises in operation direction a feed-throat (FT), the first mixingzone (MZ1), the second mixing zone (MZ2) and a die (D), wherein betweenthe first mixing zone (MZ1) and the second mixing zone (MZ2) a sidefeed-throat (SFT) is located, wherein further the polypropylene (PP) ofstep a), the thermally decomposing free radical-forming agent of stepb), and the bifunctionally unsaturated monomer(s) and/ormultifunctionally unsaturated low molecular weight polymer(s) of step c)are fed via the feed-throat (FT) and the linear polypropylene (l-PP) ofstep d) is fed via the side feed-throat (SFT).
 8. The process accordingto claim 6, wherein not more than 10.0 wt.-% of the total amount of thebranched polypropylene (b-PP) of the polypropylene composition isproduced in the second mixing zone (MZ2).
 9. The process according toclaim 1, wherein 1.0 to 6.0 parts by weight of the linear polypropylene(l-PP) are added to 94.0 to 99.0 parts by weight of branchedpolypropylene (b-PP).
 10. The process according to claim 1, wherein theresulting polypropylene composition and/or branched polypropylene (b-PP)(a) has/have a melt flow rate MFR₂ (230° C.) measured according to ISO1133 of 19.0 to 30.0 g/10 min, and/or (b) has/have a F₃₀ melt strengthfrom 4.0 to 20.0 cN and a v₃₀ melt extensibility from 240 to 300 mm/s,wherein the F₃₀ melt strength and the v₃₀ melt extensibility aremeasured according to ISO 16790:2005; and/or (c) has/have an OCS gelindex of less than 2,500.
 11. The process according to claim 1, whereinthe resulting polypropylene composition is prepared in a single stepprocess.
 12. The process according to claim 1, wherein the resultingpolypropylene composition further has (a) 95.0 to 99.0 parts by weightof the branched polypropylene (b-PP); and (b) 1.0 to 5.0 parts by weightof the linear polypropylene (l-PP) having a melt flow rate MFR₂ (230°C.) measured according to ISO 1133 of 10.0 to 50.0 g/10 min; wherein thepolypropylene composition has a melt flow rate MFR₂ (230° C.) measuredaccording to ISO 1133 from 18.0 to 35.0 g/10 min, and an OCS gel indexof less than 2,500; and wherein the polypropylene composition and/or thebranched polypropylene (b-PP) has/have a F₃₀ melt strength of more than3.4 cN and a v₃₀ melt extensibility of more than 200 mm/s, wherein theF₃₀ melt strength and the v₃₀ melt extensibility are measured accordingto ISO 16790:2005.
 13. Polypropylene composition comprising: (a) 95.0 to99.0 parts by weight of a branched polypropylene (b-PP); and (b) 1.0 to5.0 parts by weight of a linear polypropylene (l-PP) having a melt flowrate MFR₂ (230° C.) measured according to ISO 1133 of 10.0 to 50.0 g/10min; wherein the polypropylene composition has a melt flow rate MFR₂(230° C.) measured according to ISO 1133 from 18.0 to 35.0 g/10 min, andan OCS gel index of less than 2,500; and wherein the polypropylenecomposition and/or the branched polypropylene (b-PP) has/have a F₃₀ meltstrength of more than 3.4 cN and a v₃₀ melt extensibility of more than200 mm/s, wherein the F₃₀ melt strength and the v₃₀ melt extensibilityare measured according to ISO 16790:2005.
 14. Polypropylene compositionaccording to claim 13, comprising (a) 95.0 to 99.0 parts by weight of abranched polypropylene (b-PP); and (b) 1.0 to 5.0 parts by weight of alinear polypropylene (l-PP) having a melt flow rate MFR₂ (230° C.)measured according to ISO 1133 from 25.0 to 38.0 g/10 min; wherein thepolypropylene composition has a melt flow rate MFR₂ (230° C.) measuredaccording to ISO 1133 from 19.0 to 25.0 g/10 min, and an OCS gel indexof less than 2,000; and wherein further the polypropylene compositionand/or the branched polypropylene (b-PP) has/have a F₃₀ melt strengthfrom 4.0 to 20.0 cN and a v₃₀ melt extensibility from 240 to 300 mm/s,wherein the F₃₀ melt strength and the v₃₀ melt extensibility aremeasured according to ISO 16790:2005.
 15. Polypropylene compositionaccording to claim 13, wherein the polypropylene composition comprisesat least one additive (A) selected from the group consisting ofantioxidants, metal deactivators, UV-stabilizers, antistatic agents,antifogging agents, acid scavengers, blowing agents, cling agents,lubricants, nucleating agents, slip agents, antiblocking agents andmixtures thereof.
 16. Film comprising the polypropylene compositionaccording claim
 13. 17. The process according to claim 1, wherein thepolypropylene (PP) has a melt flow rate MFR₂ (230° C.) measuredaccording to ISO in the range from 1.0 to 15.0 g/10 min.
 18. The processaccording to claim 1, wherein (a) the linear polypropylene (l-PP) ofstep d) has a melt flow rate MFR₂ (230° C.) measured according to ISO1133 from 25.0 to 38.0 g/10 min, and/or (b) the linear polypropylene(l-PP) of step d) comprises two additives (A) selected from the groupconsisting of antioxidants, metal deactivators, UV-stabilizers,antistatic agents, antifogging agents, acid scavengers, blowing agents,cling agents, lubricants, nucleating agents, slip agents, antiblockingagents and mixtures thereof, and/or (c) the branched polypropylene(b-PP) obtained in step e) is free of additives (A).
 19. The processaccording to claim 1, wherein 1.0 to 3.0 parts by weight of the linearpolypropylene (l-PP) are added to 97.0 to 99.0 parts by weight ofbranched polypropylene (b-PP).
 20. The process according to claim 1,wherein the resulting polypropylene composition and/or branchedpolypropylene (b-PP) (a) has/have a melt flow rate MFR₂ (230° C.)measured according to ISO 1133 of 19.0 to 30.0 g/10 min, and/or (b)has/have a F₃₀ melt strength from 4.0 to 20.0 cN and a v₃₀ meltextensibility from 240 to 300 mm/s, wherein the F₃₀ melt strength andthe v₃₀ melt extensibility are measured according to ISO 16790:2005;and/or (d) has/have an OCS gel index of less than 2,000.
 21. The processaccording to claim 1, wherein the resulting polypropylene compositionfurther has (a) 95.0 to 99.0 parts by weight of the branchedpolypropylene (b-PP); and (b) 1.0 to 5.0 parts by weight of the linearpolypropylene (l-PP) having a melt flow rate MFR₂ (230° C.) measuredaccording to ISO 1133 from 20.0 to 40.0 g/10 min; wherein thepolypropylene composition has a melt flow rate MFR₂ (230° C.) measuredaccording to ISO 1133 from 18.0 to 35.0 g/10 min, and an OCS gel indexof less than 2,500; and wherein the polypropylene composition and/or thebranched polypropylene (b-PP) has/have a F₃₀ melt strength of more than3.4 cN and a v₃₀ melt extensibility of more than 200 mm/s, wherein theF₃₀ melt strength and the v₃₀ melt extensibility are measured accordingto ISO 16790:2005.
 22. The polypropylene composition according to claim13, wherein the the linear polypropylene (l-PP) has a melt flow rateMFR₂ (230° C.) measured according to ISO 1133 from 20.0 to 40.0 g/10min.